Dye polymers, each of which is formed of a polymer of an addition-polymerizable monomer and a dye bonded together, are conventionally known, and by various production processes, typically by radical polymerization processes, these dye polymers can be obtained from various compounds. Examples of these production processes include a process that copolymerizes a dye monomer, which is formed of a dye and an addition-polymerizable, unsaturated bond introduced therein, with another radically-polymerizable monomer (Patent Document 1 and Patent Document 2), and a process that reduces a dye, which contains a nitro group, to form an amino group, diazotizes the amino group into a radical generating group, and by using the resultant compound as a radical polymerization initiator, subjects an addition-polymerizable monomer to radical polymerization (Patent Document 3 to Patent Document 5).
In addition, a living radical polymerization process has also been developed, which is a novel and precise polymerization process that initiates polymerization from a specific initiating group. This living radical polymerization process generally means a process that stabilizes the polymerizable radical end with a stable group, causes the stable end group to dissociate under the action of heat or a catalyst to form a radical at the end of the polymer, and polymerizes a monomer at the moment of the dissociation. The existence of a compound, which has a stable group, in a polymerization system results in immediate bonding of the stable group to the polymer radical so that the radical end of the polymer is stabilized. This process prevents a bimolecular termination reaction or disproportionation reaction as a side reaction of radical polymerization and does not deactivate the radical as a reactive end, that is, a “living” radical polymerization process.
In this living radical polymerization process, the polymerization proceeds as time goes on, and based on the amount of polymerization initiating groups at the initiation of the reaction, the molecular weight of a polymer is determined and controlled, and the molecular weight distribution of the resulting polymer can be controlled very narrow (molecular weight distribution, PDI: 1 to 1.3). Upon addition of a next supply of the monomer after the completion of the polymerization, polymerization is resumed to enable block polymerization to afford a block copolymer although such block copolymerization can be hardly conducted by the conventional radical polymerization. This living radical polymerization process also features that the selection of appropriate initiating groups makes it possible to produce polymers of various higher structures, such as graft copolymers and star polymers.
Developed as specific examples of the above-described living radical polymerization process include the nitroxide mediated polymerization (NMP) process that makes use of dissociation and bonding of amine oxide radicals (Non-patent Document 1), the atom transfer radical polymerization (ATRP) process that polymerizes a monomer in the presence of a halogen compound as a polymerization initiator by using a heavy metal such as copper, ruthenium, nickel or iron and a ligand capable of forming a complex with such a metal (Patent Document 6, Patent Document 7, and Non-patent Document 2), the reversible addition-fragmentation transfer (RAFT) process that subjects an addition-polymerizable monomer to radial polymerization by using a dithiocarboxylate ester, a xanthate compound or the like as a polymerization initiator (Patent Document 8), the macromolecular design via interchange of xanthate (MADIX) process (Patent Document 9), the degenerative transfer (DT) process that makes use of a heavy metal such as an organotellurium compound, organobismuth compound, organoantimony compound, antimony halide, organogermanium compound or germanium halide (Patent Document 10 and Non-patent Document 3), and so on. Extensive research and development work is underway on the living radical polymerization process.
The use of the above-described process is considered possible to obtain a dye polymer by introducing an initiating group, which can induce living radical polymerization, into a dye and conducting living radical polymerization by using the initiating group. For example, a dye polymer formed of a pigment and a polymer bonded thereto has been obtained by the atom transfer radical polymerization (ATRP) process, in which a sulfonated chloride group or brominated alkyl group is introduced into an organic pigment and an addition-polymerizable monomer is polymerized by using, as a polymerization initiator, the resulting derivative and as a catalyst, a copper compound and a ligand capable of forming a complex with the copper compound (Patent Document 11). In accordance with the ATRP process, a polymer (pigment dispersant) having an aromatic ring at an end thereof has also been obtained by using an aromatic ring compound (Patent Document 12).
Prior Art Documents
Patent Documents
    Patent Document 1: JP-A-38-13530    Patent Document 2: JP-A-41-17063    Patent Document 3: JP-A-39-3980    Patent Document 4: JP-B-49-10690    Patent Document 5: JP-B-60-27697    Patent Document 6: JP-A-2000-500516    Patent Document 7: JP-A-2000-514479    Patent Document 8: JP-A-2000-515181    Patent Document 9: WO 99/05099    Patent Document 10: JP-A-2007-277533    Patent Document 11: JP-A-2006-16488    Patent Document 12: JP-A-2006-167674Non-patent Documents    Non-patent Document 1: Chemical Review (2001) 101, p3661    Non-patent Document 2: Chemical Review (2001) 101, p3689    Non-patent Document 3: Journal of American Chemical Society (2002) 124 p2874, ibid. (2002) 124 p13666, ibid. (2003) 125 p8720.